The fracking industry loves to argue there's no proof its gas-extraction methods cause pollution. But it works hard in Pennsylvania to keep secret any evidence that might prove the question — one way or the other.

The Marcellus Shale Coalition, the primary fracking industry lobby group in Pennsylvania and nearby states, has for two years been building a database of water testing results on private wells before gas drilling operations begin. But it only makes the information available to the gas industry, the Pennsylvania Department of Environmental Protection, and one researcher who signed a non-disclosure agreement.

Any journalists who hope to report to the public on the impacts of fracking have no hope of using the database. Its existence was reported by Marie Cusick of WITF in Harrisburg, via NPR's StateImpact Pennsylvania.